1. Field of the Invention
This invention generally relates to the field of magnetic disk drive data storage system design, and more particularly relates to power consumption reduction techniques used in the design of magnetic disk drives.
2. Description of Related Art
Magnetic disk drives that are used as mass storage in a computer system consume a significant amount of the total power needed to operate the system. Reducing the power consumed by computer systems is a design goal in many applications. Portable computers which operate from battery power, greatly benefit from reduced power consumption in any of their components. A reduction in power consumption in any computer system reduces heat dissipation requirements and increases longevity of computer components.
The challenge of reducing power consumption of a disk drive has resulted in the development of disk drive units that incorporate a variety of power savings modes. Power savings modes available in prior art designs include 1) Idle: shutting down electronic subsystems; 2) Standby: shutting down the spindle motor; and 3) Sleep: turning off all systems other than those needed to wake up the system. A description of an example set of operating modes typically found in disk drives is given below:
1) Active mode: In Active mode, the hard drive reads, writes, seeks and processes host commands. In this mode, typical hard drives consume approximately 2.0-2.5 watts.
2) Idle mode: Idle mode reduces power consumption by turning off some of the drive electronics at the expense of a short recovery time. In one common implementation, the recording head is moved to a parking position on the recording media, and the servo tracking function either is turned off, or operated at a reduced level of control. The disk remains spinning, the interface electronics remain ready to accept commands, and the drive will return to Active mode when a new command is received. The drive power is reduced to slightly less than 1 watt. Typically, the drive requires about 40 millisecond to return to Active mode.
3) Standby mode: In Standby mode, the recording heads are either unloaded or moved to a start/stop location on the recording media, the spindle motor is stopped, and most of the electronics are powered off. Power consumption is lowered to the range of 0.3 watts, but recovery time from Standby mode to Active mode is increased to a few seconds. The interface electronics remain ready to accept commands, and the drive will return to Active mode when a new command is received. Typically the drive requires between 1.5 and 5 seconds returning to Active mode. (Desktop and server drives may require up to 30 seconds recovering from Standby mode.)
4) Sleep mode: Sleep mode is entered by a specific command, and is used for long periods (hours) of system inactivity. All electronics are powered off except those needed to respond to a wake-up command, typically requiring about 0.1 watt. Recovery time is several seconds.
While the above described set of operating modes are representative of prior art disk drive designs, there are additional subsets of these modes such as, for example, some disk drives incorporate multiple versions of Idle mode. An example of idle mode subsets incorporated into prior art disk drives include:
1) Performance Idle mode: Performance idle mode is entered immediately following the completion of command processing in Active mode. Unlike conventional Idle mode, there is no entry delay. In Performance Idle, full servo performance is maintained, but some of the electronics are powered down. Subsequent commands are processed with no delay. Performance Idle mode power consumption is about 1.5-2.0 watts.
2) Fast Idle mode: In Fast idle mode, power consumption is similar to a conventional Idle mode. The recording head is moved to a parking location and the servo control turned off. Fast idle mode power consumption is in the 0.8 watt range. Recovery time to Active mode is about 40 ms.
3) Low Power (LP) Idle mode: In LP idle mode, the power consumption is reduced by 25% compared with Fast idle mode. The recording heads are unloaded from the disk, reducing power consumption to the 0.6 watt range. In LP idle mode, the drive has improved shock tolerance since the recording heads are not flying over the disk surfaces. Recovery time to Active mode is about 400 mS.
Modern magnetic disk drives typically utilize one or more magnetic disk platters that have magnetic recording media on both sides of each platter. In order to maximize the recording density on the magnetic disk platters, disk drive designs utilize recording transducer heads (commonly referred to as recording heads) which fly very close to the surface of the disk platter. Example disk drives utilize recording heads with a fly height of roughly 40 nanometers above the recording surface. Typically, each recording surface has a recording head dedicated to that surface and which is mounted on a slider for the purpose of flying the recording head at a fixed distance above the magnetic disk platter. The slider is then mounted on a suspension which is attached to an actuator to cause the slider to move across the surface of the magnetic disk platter.
The recording heads induce a drag on the spinning magnetic disk platters of an operating disk drive due to the proximity of the recording head to the platter. Each recording head produces an amount of drag, and the amount of drag is linearly related to the number of recording heads utilized in a disk drive. The drag induced by the recording head location above the magnetic disk platter is a significant source of power consumption in the disk drive. This is indicated by the power specifications for a typical prior art disk drive, which are shown in Table 1 for disk drives which use 8, 4 and 2 recording heads, respectively.
The above typical data shows that for the Low power Idle mode, in which the recording heads are unloaded (i.e., not flying above the disk), the power consumption is reduced by approximately 25-30% compared to the fast Idle mode in which the recording heads are flying over the disk. The average power savings is approximately 75 to 100 milliwatts per recording head with the recording heads unloaded versus loaded. This is a result of eliminating the drag of the recording heads on the rotating disk.
Prior art disk drives that are designed for mobile products consist of a single actuator, which positions all recording heads simultaneously. As a result, all recording heads are mounted to the single actuator. The mounting of all of a disk drive""s recording heads on a single actuator leads to the following disadvantages:
1) operating modes can not be initiated for each individual recording head on the drive, and
2) an operating shock event occurring while the recording heads are in operation affects all recording heads in the drive simultaneously as all recording heads are flying during operation.
Therefore a need exists to overcome the problems with the prior art as discussed above, and particularly for a hard drive design that utilizes more effective techniques to reduce power consumption during operation.
According to an example embodiment of the present invention, a low power hard disk drive using multiple, individually controllable actuators comprises a method for placing a recording head over a recording media within a disk drive that maintains a plurality of recording heads within a disk drive, wherein each recording head within the plurality of recording heads may be individually activated and wherein each recording head is parked when not activated, and then determines a required recording head transducer to access a requested data set, wherein the requested data set is stored within the disk drive and wherein the required recording head transducer is a recording head transducer which may access the requested data set and finally activates only the required recording head transducer to access the requested data set.
According to an example embodiment of the present invention, a low power hard disk drive using multiple, individually controllable actuators also comprises a plurality of recording heads within the disk drive, wherein each recording head within the plurality of recording heads may be individually activated and wherein each recording head is parked when not activated and also comprises a hard disk drive controller for determining a required recording head transducer to access a requested data set, wherein the requested data set is stored within the disk drive and wherein the required recording head transducer is a recording head transducer which may access the requested data set.